Generally, semiconductor devices are manufactured by repeatedly performing a series of unit processes including a deposition process, a photolithography process, an etching process, a chemical-mechanical polishing process, a cleaning process, a drying process and so on. In these unit processes, the deposition process is executed to form a film on a semiconductor substrate. The deposition process has become of particular concern in semiconductor manufacturing technology as the patterns formed on semiconductor substrates have become minute, and the aspect ratios of the patterns have increased.
Processes for forming the film on the semiconductor substrate include a chemical vapor deposition (CVD) process, a low pressure chemical vapor deposition (LPCVD) process, a plasma enhanced chemical vapor deposition (PECVD) process, and a metal organic chemical vapor deposition (MOCVD) process. Recently, an atomic layer deposition (ALD) process, a cyclic chemical vapor deposition (CCVD) process, a digital chemical vapor deposition (DCVD) process, and an advanced chemical vapor deposition (ACVD) process have been used.
In the process for forming the film, required elements are supplied to the semiconductor as raw materials for forming the film in a gas phase. Thus, a source gas is prepared including reactants comprising metal organic precursors and metal halides in addition to the required elements, then the source gas is provided to the substrate. To minimize impurities in the desired film formed on the substrate using the CVD process, organic ligands or halides combined with metal elements among the reactants provided to the substrate are decomposed so that the organic ligands or halides are removed from the substrate. On the other hand, in the ALD process, the organic ligands or halides are removed from the substrate by means of chemical exchange reactions. According to the ALD process, the required source gases are not mixed in a processing chamber. Rather, the required source gases are successively provided in the processing chamber using a pulse method. For example, when the film is formed using a first source gas and a second source gas, the first source gas is primarily provided into the processing chamber so that the first source gas is chemically absorbed on the substrate. Then, the second source gas is provided into the processing chamber such that the second source gas is chemically bonded onto the substrate.
In general, the source gas is evaporated from a liquid source, then is provided into a processing chamber by means of a carrier gas. The main parameters of the process for forming the film include deposition time, deposition pressure, the supply time of the source gas, the supply time of a purge gas, and the impurity concentration of the source gas. The impurity concentration of the film, the step coverage of the film and the uniformity of the film have become increasingly important in determining the performance of a semiconductor device as the degree of integration of semiconductor devices has increased.
U.S. Pat. No. 6,155,540 to Takamatsu et al. discloses an apparatus for supplying a source gas obtained by evaporating a liquid source. In the apparatus for supplying the source gas, after the liquid source for the chemical vapor deposition is introduced into a vaporizer by the controlled flow rate, the liquid source is sprayed by an ultrasonic atomizing device installed at the inside or the outside of the vaporizer. The liquid source is then heated and evaporated by a carrier gas.
Also, a method is provided for supplying a source gas by bubbling a carrier gas in a liquid source to form the source gas.
FIG. 1 is a schematic cross-sectional view illustrating a conventional apparatus 100 for supplying a source gas.
Referring to FIG. 1, a liquid source 10 is disposed in a sealed container 102. A heater 104 is disposed beneath the container 102 for heating the liquid source 10. A carrier gas supplying line 110 is installed such that it passes through the upper portion of the container 102, and the end portion of the carrier gas supplying line 110 is immersed in the liquid source 10 in the container 102.
The liquid source 10 is evaporated by the bubbling of carrier gas provided from the carrier gas supplying line 110 and heating of the heater 104. The vapor source prepared in the container 102 is introduced into a processing chamber 140 together with the carrier gas through a source gas supplying line 112.
Additionally, a purge gas supplying line 114 is connected to the processing chamber 140 for supplying a purge gas to purge the processing chamber.
A chuck 142 for supporting a semiconductor substrate W is installed in the processing chamber 140. A heater (not shown) is provided in the processing chamber 140 to control the temperature of the semiconductor substrate W. A vacuum pump (not shown) and a pressure control valve (not shown) are connected to the processing chamber 140 for adjusting the inner pressure of the processing chamber 140.
A flow rate control valve 120 is installed in the carrier gas supplying line 110 to control the supply flow rate of the carrier gas provided into the container 102. The source gas supplying line 112 and the purge gas supplying line 114 are connected to the processing chamber 140 through an integrated gas supply unit (IGS) 130 for controlling the supply flow rates and supply times of the purge gas and a source gas, the source gas including the vapor source and the carrier gas.
The source gas is supplied into the processing chamber 140, and is then reacted with the surface of the semiconductor substrate W so that a film is formed on the semiconductor substrate W. Un-reacted gas and reaction by-products are exhausted from the processing chamber 140 by the supply of the purge gas and operation of the vacuum pump.
When an atomic layer deposition process is performed for forming the film on the semiconductor substrate W using the apparatus 100 to supply the source gas, the carrier gas provided into the container 102 has a temperature of about room temperature (approximately 23° C.), and the liquid source 10 in the container 102 is heated to a high temperature by the heater 104. For example, when titanium alkoxide (Ti(OC3H7)4) is used as the liquid source 10 to form a titanium oxide (TiO2) film on the semiconductor substrate W, the liquid source 10 is heated to a temperature of above about 80° C. However, the deposition rate of the titanium oxide film is reduced because the temperature of the carrier gas is lower than that of the liquid source 10. Thus, the supply flow rate and the supply time of the carrier gas typically must be increased in order to deposit a film having a required thickness.
FIGS. 2 and 3 are graphs showing the deposition rate of a titanium oxide film formed by an atomic layer deposition process using a source gas provided from an apparatus for supplying source gas as shown in FIG. 1.
Referring to FIGS. 2 and 3, the deposition rate of the titanium oxide film increases in accordance with the increase in the supply flow rate and the supply time of the carrier gas. The source gas used for depositing the titanium oxide film includes the titanium alkoxide and ozone (O3), and the carrier and purge gases include argon (Ar) gases. In FIG. 2, the supply time of the carrier gas and purge time are approximately 2 seconds, respectively. In FIG. 3, the supply flow rate of carrier gas is approximately 500 sccm.
When the temperature of the liquid source is excessively increased to increase the deposition rate of the titanium oxide film, the liquid source may be thermally decomposed, thereby deteriorating certain characteristics of the liquid source. Thus, increasing the temperature of the liquid source to improve the evaporation efficiency of the liquid source may be disadvantageous. In addition, when the supply time of the source gas is extended to form a film having the desired thickness, the supply time of the purge gas typically must be prolonged, also. Hence, the throughput of the deposition process may be reduced in accordance with the supply time extensions of the source and purge gases.
Also, the source gas provided through the source gas supplying line and IGS unit has a temperature lower than that of the liquid source due to the carrier gas while the purge gas provided into the processing chamber through the purge gas supplying line of the IGS unit has a temperature substantially identical to the initial temperature of the carrier gas. Thus, the temperature of the IGS unit is lower than that of the source gas due to the purge gas. As a result, organic metal materials included in the source gas passing through the source gas supplying line and the IGS unit may be extracted as solid phases as a result of the temperature lowering of the IGS unit. The extracted organic metal materials may move into the processing chamber and serve as impurities in the film formed on the semiconductor substrate.